The Future of NANOGrav in the Post-Detection Era

In June 2023 the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration and pulsar timing array collaborations around the world published the first evidence of nanohertz gravitational waves in the form of a gravitational wave background, opening a new window on the gravitational wave universe. Pulsar timing arrays use collections of millisecond pulsars to search for gravitational waves at much lower frequencies than can be probed with ground-based and space-based interferometers. Potential sources emitting at these frequencies include supermassive binary black holes, which form in galaxy mergers, as well cosmic strings, phase transitions in the early universe, and inflation. In this talk, I will discuss the physics and astrophysics that can be probed by pulsar timing arrays in the coming decade, including what we can learn about the source of the gravitational wave background, prospects for finding gravitational waves from individual sources, and how we can use pulsar timing arrays to test gravity.